Alan,
> Though it looks weird, I think it's actually correct. th->th_sum lies
> within the packet that it inspected by in_cksum_skip. in_cksum_skip
> skips the ethernet and IP headers, but not the TCP header. So it
> consumes whatever value was previously set in th_sum. In any case, it
> will be easy to check this code by running the builtin unit tests. Just
> build the kernel with XNB_DEBUG defined, instantiate an xnb interface,
> and do "sysctl dev.xnb.0.unit_test_results".

I agress the code looks strange but is probably correct as far as it goes.
The code assumes that there aren't any IP options. I am not sure if this
is a valid assumption or not. The code also assumes packet is IPv4.
> FWIW, there is a performance problem with Xen and checksums. Whenever
> FreeBSD is used as a dom0, checksum offloading should be disabled on the
> netfronts. I don't know if the same problem exists on other OSes, but
> it might. See xnb(4) for more details about this problem.
Ok I read the CAVEATS on xnb(4). Let me play with that for a bit. I have
an ugly code patch, that works for me with out disabling checksum offloading.
Before I share, let me do a few more tests.
Larry
--
------------------------------------------------------------------------
Larry Baird
Global Technology Associates, Inc. 1992-2012 | http://www.gta.com
Celebrating Twenty Years of Software Innovation | Orlando, FL
Email: l...@gta.com | TEL 407-380-0220
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